Unloading valve for hydraulic pumps



1949. J. M. TOWLER ET AL UNLOADING VALVE FOR HYDRAULIC PUMPS Filed Feb.17, 1944 I WW 1 l Alll tatentecl Aug. 9, 1949 UNLOADING VALVE FORHYDRAULIC PUMPS John Maurice Towler, Harrogate, and Frank HathornTowler, Otley, England, assignors to Electraulic Presses Limited,Rodley, England Application February 17, 1944, Serial No. 522,843 InGreat Britain March 15, 1943 6 Claims. 1

This invention relates to an unloading valve for use with either asingle reciprocating ram pump having two or more rams or with aplurality of single or multi-ram pumps, said valve being of the kindembodying a valve member in the form of a sliding plunger which is movedagainst a predetermined load by hydraulic pressure to unload in sequenceeither the pump chambers of a multi-ram pump or to unload, also insequence, a group of two or more pumps by bypassing the delivery of eachsuch pump in turn. An unloading valve of this character is described inthe specification of our U. S. Patent No. 2,247,261.

One of the principal uses of an unloading valve of the kind with whichthis invention is concerned is to enable a predetermined pressure to \bemaintained in a hydraulic system supplied with pressure liquid by one ormore continuously running pumps.

One such system is one which embodies a moulding press in which the workhas to be maintained under full pressure for an appreciable period.Theoretically, when the full pressure behind the press ram has beenreached, such pressure should be maintained without further pumping, butin practice there is always a cer tain amount of leakage of pressurepast the ram so that unless make-up liquid is occasionally supplied, thepressure behind the ram will slowly fall.

The unloading valve of our prior patent will automatically operate tocompensate for this leakage but in doing so the valve plunger is free tomove sufficiently to load all the pump chambers or pumps in the serieswhereas it is only required that one of said chambers or pumps shall bemomentarily loaded to restore the pressure to the figure required.

As soon as loading occurs the resulting build up in pressure in thesystem will at once move the plunger in the unloading direction and byreason of the freedom of movement above referred to and the resultingsensitiveness of the plunger to variations in pressure in the operatingliquid the tendency will be for the plunger to dither or oscillaterapidly.

The object of the present invention is to provide means in an unloadingvalve of the type specified which will limit the loading movement of thevalve plunger when full pressure has been attained so that only therequired number of pump chambers or pumps necessary to supply occasionalmake-up liquid to compensate for normal leakage will be loaded, theremaining one or more pump chambers or pumps remaining unloaded untilfall in pressure has occurred which is substantially greater than couldresult from normal leakage. y

7 An unloading valve according to the present invention has means whichnecessitates a substantial rise in the pressure of the operating liquidto effect the last part of the unloading stroke of the valve plungerwhereby said valve plunger is rendered capable of moving to load atleast one of the pump chambers or pumps against an opposing pressure,afiorded by the operating liquid, which is substantially greater thanthe pressure which the plunger is capable of moving against to load theremaining one or more pum chambers or pumps so that said first mentionedpump chamber or pump can 'be cut in and out rapidly to supply make-upliquid to a hydraulic system, for example to counteract normal leakage,with the other one or more pump chambers or pumps remaining unloaded.

In the preferred embodiment of the present invention the means abovereferred to consists of a piston of larger area mounted on and so as tohave independent movement relative to a ram of smaller area, the firstpart of the valve plungers unloading stroke being effected by both thepiston and ram acting together and the last part of the same stroke bythe ram alone whereby a rise in the pressure of the operating liquid hasto take place before the smaller area ram can overcome the pressureopposing the valve plunger so that whereas the opposing pressure canforce the valve plunger and ram back against said higher pressure toload the pump chamber or pump that was last to be unloaded, asubstantial fall in the pressure of the operating liquid must occurbefore said load can force the valve plunger and piston back owing tothe larger area of said piston.

In a further embodiment of the invention the means specified consists ofan additional spring load which comes into action to supplement theopposing efiort of a main spring only during the last part of theunloading movement of the valve plunger, so that again a substantialincrease must occur in the pressure of the operating liquid before theplunger can be moved to overcome the additional load. Said additionalload will act to move the plunger in the return direction against theincreased pressure to load the number of pump chambers or pumps requiredto supply the make-up liquid, but, as in the first embodiment, theremaining pump chambers or pumps will 3 remain unloaded until asubstantial fall in the pressure of the operating liquid takes place.

In the drawings:

Fig. 1 is a vertical longitudinal section through a valve according tothe invention.

Fig. 2 is a vertical longitudinal section through a portion of the valveillustrating a. modifiedembodiment of: the invention.

In Fig. 1, the pump illustrated comprises a pump body I which is boredto provide three pump bores 2, 3 and 4.

On opposite sides of each pump bore and at the inner end thereof aresituated two: transverse outlet passages, the passages 55-, W and- Bbeing the normal discharge outlet for the pumped liquid to pass thedelivery valves atoa commondelivery main b and the opposing passages 8;9: and ll) being the by-pass passages.

The by-pass passages open into a transverse bore H in the pump bodywhich is machined to receive a packingless piston: valve [:2 Withi a fitwhich while permitting. the piston: valve: to move freely thereinwill=yet prevent the: leakagesof; the pressure liquid.

The'spindle; which constitutes the piston valve has a passage l3extending longitudinally through itsv centre, whichpassagei's open atboth ends: toexhaust.

In the example: illustrated the valve spindle is provided with three"circumferential reduced portions I' l, l5 and t6;- These reduced.portions are connected by radial passages t1; with the hollow centrepassage 13 of. the valve spindle;

The piston'valve is showndn; the drawing. in its partially open.positionbut. is normally held. in the closed position by aspringi l9=which acts against the open or exhaust end of. the valve through athrust washer 2:05. the load on the: spring, being adjusted by ascrewor-other means. not.- shown.

With the construction above: described endwise movement of the: pistonvalve against the spring l9 brings. the; reduced portions :4, l5 and H5inturnintoregistration: with the open. ends of the by-pass passages 8 9and I'll respectively thus placing the corresponding, pump bores incommunication with the passage t3- inv the valve and so to exhaust.

The reduced. portions ofthevalve spindle are so arranged that, as the.valve is made to traverse the by-pass passages by the actuating ram thepassage 8 is first uncovered tosuch anextentthat the pressure in theassociated pump bore is not sufiicient to lift the delivery valvea andtherefore that pump ram stops. pumpingt As the. pressure rises in thedelivery main 11,, the spindle is moved further over so. as completelyto unload the pump bore 2 and the second reduced. portion l5 of thespindle begins to uncover. the intermediate by pass passage 9 connectedto the intermediate pump" bore 3 so that the pressure in that pump boreisreleased to such an extent that the inter mediate ramv ceases to pump.Finally, as the pressure in the delivery main increases still further,the valve spindle ismoved' partially to uncover the third by-passageIll, thereby reducing the delivery of the third ram up to such a pointthat it ceases pumping. As the pressure drops, the sequence is reverseduntil the three rams are pumping again.

The endwisemovement of the piston valve I-Z'is eflected intwo stages bytwo independently mov-- able pistons 2| and 22" of difierent areas. Thelarger piston 21 is'mounted on the smaller'piston' 22 along which it isfree to slide and within a cyl' i'niler 23, the interior of which isopen by means of inlet 24 with the delivery main of the pump or pumps tobe controlled. The piston 2| acts with the piston 22 to perform thefirst part of the unloading stroke of the plunger. The position of thevalve plunger at the end of this partial unloading stroke is shown inthe drawing and in this position; the two near bores 2 and 3 areunloaded whilst the third bore is still loaded-L As the area of thepiston 22 is less than the area of the piston 2! a correspondinglygreater pressure will be required to move it. When this pressure in thecylinder 23, has, however, been reached the piston 22 will operateindependently of the piston 2F to move the valve plunger tounloadthethird pump bore 4.

Asa resultoi. thesmaller area of the piston 22 the: spring; It iscapable of moving the plunger back to load the third pump bore 4 againstthe increased pressure of the, operating liquid but further returnmovement of the plunger to load the remaining: pump chambers: cannot.take:- place until thepressure of the operating liquid. has fallen to asubstantial extent owing to' the: higher resistance oilered by thelarger area of the. piston: 2|

Inthe modified embodiment shown inv Fig; 2 the-same efiect canbeattain'ed by dispensing. with the piston 21 andiusing asingle piston,-and. providing an additional spring 25 of shorter length than the springt9 which additional spring. is compressed to supplement the opposingforce of the main spring l'9 only during the latter part of the valveplungers stroke. To move the: valve plunger to unload the third pumpbore will thus require a rise inpressure inthe cylinder 23 and thereturn movement of the valve plunger to load the secondv and firstpumpbores will not take place until the pressure of the liquid hasfallen considerably.

Although in the above description the unloadi'ng valve has beendescribed as being used for unloading the pump chambers of a singlemultiram pumpit is equally capable of use in' unloading in sequence twoor more pumps. The only material alteration in the construction. of thevalve is that the valve plunger is mounted in a separate valve blockhaving two or more chambers each connected to the delivery manifold of apump; Thus when the part communicating with the delivery of the pump isopened the delivery of that pump is by-passed to the pump reservoir orin other words is unloaded.

The supply of pressure liquid to the cylinder which actuates theunloading valve may be effected in various manners, without departingfrom this invention. Furthermore, a number of unloading valvesconstructed as described in the previous embodiments may be madetooperate in sequence, when actuated bya' common pressure supply, bymaking" the actuating pistons of different area or'making; theopposlngsprings of different strength.

What we claim is? I. An unloading valve" for a plurality of pressureliquid delivery chambers connected to a de livery main, comprising abore open' toexhaust, passages communicating with said bore, and con-'nected to said chambers; a valve plunger slid'able in said bore having apassage extending longitudinally therethrough, circumferential reducedportions arranged to register in sequence with said passages in themovement of the plunger said bore and openings connecting said reducedportions with said passage of the plunger, whereby the delivery chambersare sequentially connectable to exhaust to unload the same, said plungerbeing normally held in a position wherein the reduced portions thereofare isolated from said passages, a plurality of pistons associated withsaid plunger, at least one of which causes the plunger, upon attainmentof a predetermined pressure of the liquid in the delivery main, to movefrom said normal position thereof through an initial part of its stroketo sequentially cause some of said reduced portions to register withsome of the passages aforesaid to unload some of the delivery chambers,and only one of which pistons causes the plunger to effect the finalpart of its stroke only upon a further and substantial increase in thepressure of the liquid.

2. An unloading valve for a plurality of pressure liquid deliverychambers connected to a delivery main, comprising a bore open toexhaust, passages communicating with said bore and connected to saidchambers, a valve plunger slldable in said bore having a passageextending longitudinally thcrethrough, circumferential reduced portionsarranged to register in sequence with said passages in the movement ofthe plunger in said bore and openings connecting said reduced portionswith said passage of the plunger, whereby the delivery chambers aresequentially connectable to exhaust to unload the same, means forholding the plunger in a normal position wherein the reduced portionsthereof are isolated from said passages, a plurality of pistonsrespectively of different area, associated with said plunger, at leastthe piston of larger area, upon attainment of a predetermined pressureof the liquid in the delivery main, causing the plunger to move fromsaid normal position thereof through an initial part of its stroke tosequentially cause some of said reduced portions to register with someof the passages aforesaid to unload some of the delivery chambers, andonly the piston of smaller area, upon a further and substantial increasein the pressure of the liquid, causing the plunger to eifect the finalpart of its stroke, whereby the remaining chamber is caused to beunloaded and loaded while the other chambers remain unloaded.

3. An unloading valve for a plurality of pressure liquid deliverychambers connected to a delivery main, comprising a bore open toexhaust, passages communicating with said bore and connected to saidchambers, a valve plunger slldable in said bore having a passageextending longitudinally therethrough, spaced circumferential ree ducedportions arranged to register in sequence with said by-pass passages inthe movement of the plunger in the bore and openings connecting saidreduced portions with said passage of the plunger, whereby the deliverychambers are sequentially connectable to exhaust to unload the same,means for resisting movement of the plunger from a normal positionwherein the reduced portions of the plunger are isolated from thepassages, means associated with the plunger comprising a plurality ofpistons of different crosssectional areas, at least one of which isoperable in response to a predetermined increase of the pressure in thedelivery main and moves the plunger from said normal position thereof inopposition to said movement resisting means, and means effective at apredetermined point of the unloading stroke of the plunger to increasethe resistance to the movement of the plunger whereby a further increasein the pressure of the liquid is required, to further move said plunger,the said piston of smaller area. efiective only upon a fur- '6 therincrease in the pressure of the liquid, moving the plunger to effect thelast part of its stroke for unloading the delivery chambers.

4. An unloading valve for a plurality of pros sure liquid deliverychambers connected to a delivery main, comprising a bore open toexhaust, passages communicating with said bore and connected to saidchambers, a valve plunger slidable in said bore having a passageextending longitudinally therethrough, circumferential reduced portionsarranged to register in sequence with said passages in the movement ofthe plunger in said bore and openings connecting said reduced portionswith said passage of the plunger, whereby the delivery chambers aresequentially connectable to exhaust to unload the same, means forholding the plunger in a normal position wherein the reduced portionsthereof are isolated from said passages, a cylinder open to the pressureof the liquid in the delivery main, a piston in said cylinder associatedwith the plunger for causing this latter to perform part of itsunloading stroke upon a predetermined increase in the pressure of theliquid in the delivery main, and a second piston of smaller area in thecylinder independent of the first piston and associated with the plungerfor causing this latter to complete its unloading stroke only upon afurther and substantial increase in the pressure of the liquid.

5. In combination with a plurality of pressure liquid delivery chambersconnected to a delivery main, an unloading valve comprising a pluralityof inlets communicating with said delivery chambers, a reciprocableplunger adapted to sequentially connect said inlets to exhaust andnormally maintained in a position to close said inlets, a piston formoving said plunger from said normal position thereof through an initialpart of its stroke upon attainment of a predetermined pressure of theliquid in the delivery main, to sequentially connect some of the inletsto exhaust to unload some of the delivery chambers, and a second pistonindependent of said first named piston for moving the plunger to effectthe final part of its stroke only upon a further and substantialincrease in the pressure of the liquids, whereby to cause at least oneof the delivery chambers to be unloaded and loaded while the otherchambers remain unloaded.

6. In combination with a plurality of pressure liquid delivery chambersconnected to a delivery main, an unloading valve comprising a pluralityof inlets communicating with said delivery chambers, a reciprocableplunger adapted to sequentially connect said inlets to exhaust to unloadsaid delivery chambers and normally maintained in a position to closesaid inlets to load said chambers, and means responsive to the pressureof the liquid in the delivery main and loading means associated with theplunger cooperating to cause the plunger to effect its stroke in twodistinct stages as substantially diiferent pressures of the liquid,whereby to cause the plunger to unload and load at least one of thechambers while the other chambers remain unloaded, said means comprisingtwo pistons, associated with said plunger and mounted for conjoint andrelative movement, said pistons being actuable together to effect thestroke of the plunger in its first stage, and only one of which isactuable to effect the stroke of such plunger in its second stage.

JOHN MAURICE TOWLER. FRANK HATHORN TOWLER.

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